Datatronics Measuring Transformer Distributed Capacitance

This article is a general discussion of distributed capacitance, Cd, in transformers with emphasis on measurement. We will discuss how capacitance occurs, references to formula for calculating, how capacitance is modeled, how Cd is measured (with three cautionary notes) and guidelines to aid in evaluating / measuring Cd.

Capacitance in a transformer winding cannot be avoided. The voltage difference between turns, between winding layers and between windings to core create these parasitic elements. In general, part of the designers' task is to keep capacitance to a minimum. On rare occasions winding capacitance is increased to reduce ringing in switching transformers.